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TT: Tiefe Temperaturen

TT 30: Postersitzung IV: Kritische Ph
änomene, Quantenstörstellen, niederdimensionale Systeme

TT 30.44: Poster

Donnerstag, 11. März 2004, 14:30–19:00, Poster A

Electron Spin Resonance of the Kondo-ion itself: evidence for a locally critical quantum phase transition — •Jörg Sichelschmidt, Julia Ferstl, Christoph Geibel, and Frank Steglich — Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str.40, 01187 Dresden

Below the Kondo temperature T_K Electron Spin Resonance (ESR) usually is not observable from the Kondo-ion itself because the characteristic spin fluctuation energy results in a huge width of the ESR line. The Kondo-ion Yb³⁺ in the heavy fermion metal YbRh₂Si₂ seems to be an exception. Here definite ESR spectra due to Yb³⁺ spins have been observed below T_K [1]. This proves the local character of the Yb³⁺ spins below T_K and provides evidence for the localized moment scenario of quantum criticality [2]. We present the ESR results on single crystalline YbRh₂Si₂ doped by La or Ge tuning the system through the zero-field quantum critical point.

[1] J. Sichelschmidt et al., Phys.Rev.Lett. 91, 156401 (2003).

[2] Q. Si et al., Nature 413, 804 (2001); J. Custers et al., Nature 424, 524 (2003).